The present invention relates to an imaging device which has an organic layer (photoelectric conversion layer) generating electric charges in accordance with received light and converts a visible light image to electrical signals. The invention more specifically relates to an imaging device capable of suppressing adverse effects of any defect in a protective film for protecting an upper electrode (counter electrode).
Solid-state imaging devices (so-called CCD sensors and CMOS sensors) in which photodiode-containing pixels are arranged on a semiconductor substrate such as a silicon (Si) chip and signal charges corresponding to photoelectrons generated in photodiodes of the respective pixels are acquired in CCD and CMOS readout circuits are widely known as image sensors utilized in, for example, a digital still camera, a digital video camera, a camera for a cellular phone and a camera for an endoscope.
In recent years, a solid-state imaging device including an organic photoelectric conversion layer which uses an organic material and generates electric charges in accordance with received light has been studied.
A solid-state imaging device having an organic photoelectric conversion layer includes pixel electrodes formed on a semiconductor substrate having signal readout circuits formed therein, the organic photoelectric conversion layer formed on the pixel electrodes, a counter electrode (upper electrode) formed on the organic photoelectric conversion layer, a protective film formed on the counter electrode for protecting the counter electrode, color filters and the like.
In the solid-state imaging device, a bias voltage is applied between the pixel electrodes and the counter electrode to cause excitons generated in the organic photoelectric conversion layer to be separated into electrons and holes, and signals corresponding to electric charges of the electrons or holes transferred to the pixel electrodes according to the bias voltage are acquired in CCD or CMOS signal readout circuits.
In such a solid-state imaging device having an organic photoelectric conversion layer, the organic photoelectric conversion layer is known to deteriorate due to, for example, moisture and oxygen, and various methods for suppressing the deterioration of the organic photoelectric conversion layer have been proposed (see JP 2004-165512 A and JP 2006-245045 A).
JP 2004-165512 A discloses an organic photoelectric conversion element which includes an organic layer disposed between two electrodes, one of which is translucent, and generating electric charges in response to irradiation with light, the organic layer having a surface protective layer formed on its surface, and the surface protective layer including an inorganic sealing layer formed by a vapor deposition process and a resin layer formed on the inorganic sealing layer. The inorganic sealing layer has an internal stress of −1 GPa to +1 GPa. In this case, the positive value indicates tensile stress and the negative value indicates compressive stress.
JP 2006-245045 A discloses a photoelectric conversion layer-stacked solid-state image pickup element in which a protective layer made of an inorganic material is formed on a transparent counter electrode and which makes use of an organic semiconductor.
It is disclosed that the inorganic material making up the protective layer is silicon oxide, silicon nitride or silicon oxynitride and the protective layer is formed by plasma CVD.